This invention relates to the production of a pressure-sensitive carbonless copy system and in particular to a system using a transfer coating composition containing a solution of an alkyl bis-(2,4-dinitrophenyl) acetate in a carrier liquid which composition is applied to a substrate.
Carbonless copy paper, briefly stated, is a standard type of paper wherein during manufacture the backside of the paper substrate is coated with what is referred to as a CB or transfer coating. The CB coating contains one or more color precursors generally in capsular form. At the same time the front side of the paper substrate is coated during manufacture with what is referred to as a CF or color-developing coating, which contains one or more color developers capable of producing a color with the color precursors. Both the color precursors and color developers remain in the coatings on the respective back and front surfaces of the paper in substantially colorless form. This is true until the CB and CF coatings are brought into overlying relationship and sufficient pressure, as by a typewriter, is applied to rupture the CB coating to release the encapsulated color precursor. At this time the color precursor contacts the CF coating and reacts with the color developer therein to form a colored image. Carbonless copy paper has proved to be an exceptionally valuable image transfer media for a variety of reasons one of which is the fact that until a CB coating is placed next to a CF coating both the CB and the CF are in an inactive state as the co-reactive color-forming elements are not in contact with one another. U.S. Pat. Nos. relating to the production of carbonless copy transfer or developer coated paper products which have been commercially successful are as follows: 2,712,507 (1955) to Green, 2,730,456 (1956) to Green et al, 3,455,721 (1969) to Phillips et al, 3,466,184 (1969) to Bowler et al, 3,672,935 (1972) to Miller et al.
A product which is in an advanced stage of development and commercialization at this time and which is available in some business sectors is referred to as self-contained paper. Very generally stated, self-contained paper refers to an image transfer system wherein only one side of the paper needs to be coated and the one coating contains both the color precursor, generally in encapsulated form, and the color developer. Thus when pressure is applied, again as by a typewriter or other writing instrument, the color precursor capsule is ruptured and reacts with the surrounding color developer to form an image. Both the carbonless paper image transfer system and the self-contained transfer system have been the subject of a great deal of patent activity. A typical autogeneous record material system, earlier sometimes referred to as "self-contained" because all elements for making a mark are in a single sheet, is disclosed in U.S. Pat. No. 2,730,457 (1956) to Green.
The aforementioned patents disclose systems using oil solutions of basic color precursors, such as the organic lactones, as the encapsulated color-forming material in combination with acidic electron acceptor coated developer sheets. Kan et al in U.S. Pat. No. 3,432,327 (1969) in Table 1 discloses a number of color-developing pairs which react to form colors in the presence of a hydrophilic liquid. In contrast, the micro-encapsulated color-forming materials of the instant invention are oil solutions of acidic color precursors, i.e., the alkyl bis-(2,4-dinitrophenyl) acetates and the color developer sheet contains a strong base, i.e., a base having a pK.sub.b below 4.8. Using the oil solutions of color-forming materials of the invention, micro-encapsulation of these solutions can be accomplished using known commercial processes. Microcapsules very stable to loss of internal contents or aging may be produced.